Is Heat Training the Same as Altitude Training for Runners?

Altitude is a mythical word in the running community. Experts tout it as a panacea for the distance runner’s soul, a magical feat of air pressure that (legally!) changes the very composition of your blood. Even those born without the incredible genetics of the Kenyans and Ethiopians who made its effects famous often see major performance boosts once they train in locales between 5,000 and 8,000 above sea level.

Today, towns in that topographical sweet spot comprise some of the hippest training venues in the United States: Boulder, Colorado; Flagstaff, Arizona; Albuquerque, New Mexico; and Mammoth Lakes, California, just to name a few. Elites (and those who dream of hearing that word) flood these towns for the simple fact that the thin air increases the quantity of oxygen-carrying red blood cells. In theory, this turbocharges your cardiovascular engine, leading to performance gains when you race at sea level.

For the majority of the U.S. population, training at altitude is a rare treat. Heat, on the other hand, we have in spades.

While many runners dread running in the heat, done right, it comes with quite a few benefits. Research shows heat-training can:

• Increase cardiac output (the quantity of blood pumped by the heart)

• Increase plasma volume (the liquid component of your blood)
• Increase VO2 max (the maximum amount of oxygen your body can take in and use during exercise)

• Lower your internal thermostat

This is great news for the many road racers gearing up for a fall marathon and younger people putting in the miles for fall cross country. Making heat work for you, however, takes more than laying out poolside.

If your mom used to warn you about the risks of running around in the middle of the summer, she wasn’t wrong.

Extreme temperatures increase the stress on your body many-fold. Blood that might normally be used to power your muscles is redirected to your skin to make sweat that’ll help you thermoregulate. As your sweat rate increases, so does the risk for significant dehydration—cognitive performance can decline after a two percent drop in bodyweight.

As you run in hot conditions, your body’s core temperature steadily increases. This leads to a phenomenon called cardiac drift, in which your heart rate (number of beats per minute) rises as your stroke volume (amount of blood pumped out of your heart) decreases. In other words, your heart is working harder but less efficiently.

Humidity amplifies this effect, reducing the cooling effect of sweat as it pools on your skin instead of evaporating. You feel thirsty, strained and hot. The end result is that a given pace is more difficult to maintain. And if you’re racing, good luck: the faster the pace, the higher the magnitude of these effects.

Eight to 14 days. Your body is clever. Expose it to a given stimulus enough and it will adapt out of necessity. Joshua Guy and his colleagues published an article in the journal Sports Medicine looking at this very topic and found that after eight to 14 days of heat exposure, athletes exercised with lower heart rates than before at the same speed, sweated earlier and had lower core temperatures. These adaptations to heat training made the athletes more efficient in all conditions.

This seemed to confirm the findings of Santiago Lorenzo’s groundbreaking 2010 study. The then-University of Oregon professor found that after a 10-day exercise protocol in the heat (100 degrees), the heat-trained athletes increased their VO2 max and power output by 8 percent and 5 percent, respectively, in hot conditions.

The bigger surprise was their VO2 max, time trial performance and power output at lactate threshold were also all five to six percent higher than before. Plasma volume and maximal cardiac output were also up six to nine percent for the heat trained group. The control group training in 55-degree weather showed no significant gains in any of these categories.

If you’re planning to run a race in hot conditions, heat training will help your performance. Even if you’re not training for a toasty race, the benefits heat training provides will help your body run more efficiently in any temperature.

You know the old saying, “nothing new on race day”? That’s true for climate, too. While it’s impossible to exactly mimic the weather conditions for any given race, if you’re not used to running in the heat and/or humidity, your pace (and overall experience) will suffer drastically if you’re headed to a warm race without the proper training.

Races like Florida’s Walt Disney World Marathon or Miami Marathon, despite being held in January, can see temperatures up to eighty degrees. This is especially tough for runners traveling from up north who have been doing all their training in the thick of winter.

So, what’s a runner to do?

Run in areas that have water fountains or carry a handheld water bottle. If you have the option, bring the electrolytes! Dehydration is a guarantee during the hotter months, but total water lost is less critical than intracellular hydration, which can be maintained by ingesting small to moderate amounts of fluids during exercise. (This is most evident in big city marathons, where elites may lose three to six percent of their body weight from dehydration but not slow down). If you have the option to mix electrolytes with your water, all the better. Salt, magnesium, and potassium help get water into your cells and replace what’s lost during sweating.